The present invention relates to pneumatic tires for use on iced and snowed road surfaces and, more particularly, to a pneumatic tire suitable for use on iced and snowed road surfaces which can improve iced road surface running performance and uneven wear resistance.
In general, pneumatic tires for use on iced and snowed road surfaces have a tread surface on which a block pattern is formed. A ground contact face of each of the blocks has a plurality of sipes extending in a width direction of the tire. The tread rubber portion consists of low hardness rubber. The edges of the blocks and the sipes provide a high scratching effect and a high water removing effect while a high friction force by adhesion of the tread rubber portion allows a larger ground contact area of the tread surface to be obtained, thereby showing high iced road surface running performance.
In recent years, anti-lock braking systems have come into use, and are mounted on a variety of vehicles. During braking, vehicles employing a conventional braking system keep the ground contact surface of the tire in the same position (the same block portions of the tread surface contact a road surface), whereby ice and/or snow adhering to the blocks of the ground contact surface and entering into the sipes is melted by friction heat produced during sliding on a snowed and iced road surface, and the blocks surely come into contact with the snowed and iced road surface. Vehicles employing an anti-lock braking system, however, always change the ground contact surface of the tire during braking, thereby ice and/or snow adhering to the blocks and entering into the sipes can not be fully melted, resulting in that the ground contact area of the blocks against a snowed and iced road surface is reduced and the edge effect of the sipes is lowered. Therefore, a distance running during braking tends to be longer and there is a problem of lowering iced road surface running performance.
Pneumatic tires have also been mentioned that uneven wear resistance of blocks is lowered due to lowering of block rigidity by formation of a plurality of sipes on the blocks.